While in rural areas, septic tank systems are, typically, provided for the treatment and dispersal of waste, in urban and suburban areas, sewer main systems are provided for conveyance and disposal of wastes prior to treatment and dispersal. Such sewer main systems service residential, commercial, and industrial units.
Sewer main lines, typically, are laid horizontally beneath the ground. While circumstances, such as deterioration over time and subjection to extremely high pressures, can occasion the need for replacement or repair of a sewer main, once a sewer main conduit is in place, it is lying on a bed at the bottom of an excavation and is not subject to major settling.
When a new location along a service main line is to be provided for, the area above the sewer main is excavated and a T is installed in the main. Such connection locations can be installed at various spaced locations along the main to provide access to a multiplicity of individual units.
Typically, such T connections extend generally vertically, from the main line as is illustrated in FIG. 1 of the drawing figures. A conduit mated to such a T coaxially therewith to provide service to, for example, an individual residence angles off of the axis of the T more horizontally in order to provide a duct over the full distance from the unit being serviced to the main line.
Such individual branch connections are, frequently, extended from a main line at some significant time after the installation of the main itself. When excavation is performed to install such a branch, after the installation is completed, the hole is filled with loose earth. When earth is filled into the hole, excavated for installation of the length of the branch line pipe, downward pressure is brought to bear upon the generally horizontal portions of the line. Such pressure is, in turn, conveyed to the vertical portion of the branch line and the T intersecting the sewer main. While the full application of the force vector may not be completely vertical, at least a component thereof is applied in a direction along the axis of the T.
This force vector causes problems as the branch settles. As previously indicated, the main line is seated on a substantially stable bed. This is so, since the main line is, tpyically, laid at the bottom of the excavation and on the top of already-settled earth. As settling of the earth fill dumped into the hole after the branch line is installed occurs, the T and vertical portion of the branch line will tend to be urged into the main line. The consequence of this force is, at a minimum, a tendency to incur minor cracking. In some cases, however, complete fracture at the Location at which the T exits from the main line results.
It is to these problems of the prior art that the present invention is directed. It is a mating structure which permits the installation of a branch line for servicing of a residence, a commercial unit, or an industrial structure without consequent cracking or fracture at the interface between the service connection and the main service line.